1. Field of the Present Invention
The invention relates to a flow meter, particularly the flow-meter having two pressure sensing devices.
2. Description of Prior Act
Shown in FIG. 1 is the conventional type flow meter (10) having a venturi tube structure formed inside the tubular main-body wherein the inlet (13) of the tubular main-body has a convergent inner diameter while the outlet (14) of the tubular main-body has a divergent inner diameter, and a transitional neck portion is formed between the inlet portion (13) and the outlet portion (14) so as to form the venturi tube structure inside the tubular main-body (11).
As for the application, the major function of the conventional flow meter (11) is to measure pressure head (P1) at the inlet (13) and the pressure head (P2) at the outlet (14) near the neck of the venturi tube, and obtain the value of pressure difference (P1−P2) between the fluid pressure at inlet (13) and outlet (14), and then an microcomputer is employed for converting the pressure difference (P1−P2) into flow rate and flow speed measurement which are then displayed by digital display unit.
Moreover, in order to measure the pressure difference (P1−P2) existing near the neck portion of the tubular main-body (11) a platform (12) is provided on the outer surface of the tubular main-body (11) having a small penetrating hole (15) arranged on the platform (12) and connected to the convergent portion of the inlet (13) of the tubular main-body; And, a recession is formed on the platform (12) for accommodating and mounting a pressure difference sensing device (18) which can sensing the fluid pressure at the divergent portion of the tubular main-body (11) through the penetrating hole (16) which is arranged as close as possible to the neck portion of the tubular main-body (11).
Meanwhile in order to enable the upper side of the pressure difference sensing device (18) to sense the pressure head (P1) at the fluid inlet (13) transmitted through the penetrating hole (15), a passage groove (19) is formed on the surface of the platform (12), and is connected to the penetrating hole (15) and upper side of the pressure difference sensing device (18), and then a cover plate (17) is tightly mounted on the upper side of the platform (12) that the upper side and the lower side of the pressure sensing device (18) can separately sense the pressure head (P1) at the inlet (13) transmitted through penetrating hole (15) and the pressure head (P2) at the outlet (14) near the neck portion transmitted through penetrating hole (16) to obtain the pressure difference (P1−P2) which shall be transmitted to the microcomputer for calculating the flow rate and flow speed.
However, this type of conventional flow meter (10) has three drawbacks as follows:
First, the conventional type flow meter (10) employs only one sensing device (18) to measure the pressure difference (P1−P2) produced at a point near the neck portion of tubular main-body (11). Since the upper side and lower side of the pressure difference sensing device (18) both have to sustain the pressure head (P1) and pressure head (P2) at the same time, malfunction always occurs due to inability of sustaining the pressure difference variation, and the service life of the conventional type flow meter (10) is therefore largely reduced to result in a poor economic effectiveness.
Second, on the upper side of the platform (12) of the tubular main-body (11) of the conventional type flow meter (10) a horizontal passage groove (19) must be provided. However, since the passage groove (19) is perpendicular to the penetrating hole (15) on the platform a distortion of measurement of the pressure head (P1) sensed by the pressure sensing device (18) is always resulted in, and actually the flow rate and flow speed measured by the conventional type flow meter are inaccurate.
Third, since a passage groove (19) is formed on the upper side of the platform (12) of the conventional type flow meter (10), a cover plate (17) must be mounted on, and tightly seal the upper side of the platform (12). However, the pressure head (P1) at the fluid inlet (13) transmitted through the penetrating hole (15) on the platform (12) is sometimes greater than the fastening force for tightly holding the cover plate (17) on the platform (12), that results in the damage or crack of the cover plate (17) due to inability of sustaining the pressure head (P1). This will cause the failure of operation of conventional type flow meter (10).